It is generally known that a rotation speed sensor built-in type wheel bearing apparatus rotationally supports a wheel of a vehicle with respect to a suspension apparatus, controls an anti-lock braking system (ABS) and detects a rotational speed of a wheel. Such a bearing apparatus generally includes a sealing apparatus arranged between inner and outer members rotating relative to each other via rolling elements, a magnetic encoder integrated with the sealing apparatus (having magnetic poles alternately arranged along its circumference) and a rotation speed sensor to detect change of magnetic poles of the magnetic encoder.
Generally, the rotation speed sensor is mounted on a knuckle that forms part of the suspension apparatus after the wheel bearing apparatus is mounted on the knuckle. A wheel bearing apparatus with a rotation speed detecting apparatus of the built-in type, that is compact and can simplify complexity of an air gap adjusting operation between the rotation speed sensor and the magnetic encoder, has been recently proposed.
A structure shown in FIG. 12 is known as one example of a wheel bearing apparatus of the rotational speed detecting apparatus built-in type. This wheel bearing apparatus includes seals (not shown) arranged between an outer member 51 and an inner ring 52. A protective cover 53 prevents leakage of grease sealed within the wheel bearing and entry of foreign matter into the wheel bearing.
A pulser ring 54 is press-fit onto the outer circumference of the inner ring 52. The pulser ring 54 has a supporting member 55 and a magnetic encoder 56. The supporting member 55 is press-formed from steel sheet as an annulus with an L-shaped cross-section. The magnetic encoder 56 integrally adhered to the supporting member 55. The supporting member 55 has a cylindrical fitting portion 55a press-fit onto the outer circumference of the inner ring 52. An upright portion 55b extends radially outward from the fitting portion 55a. The magnetic encoder 56 is integrally adhered to the upright portion 55b, via vulcanizing adhesion.
The protective cover 53 is press-fit into the inner circumference of the outer member 51 to close an opening of the outer member 51. The protective cover 53 is press-formed from austenitic stainless steel sheet with a substantially flanged disc-shaped configuration. It has a cylindrical fitting portion 53a adapted to be press-fit into the inner circumference of the outer member 51. A disc-shaped shield portion 53b radially inwardly extends from the fitting portion 53a. The disc-shaped shield portion 53b opposes the magnetic encoder 56 via a small axial gap. A bottom portion 53d (FIG. 13) extends from the shield portion 53b via a bent portion 53c. 
The detection portion of the rotation speed sensor 57 is arranged opposite to the protective cover 53 close to or in contact with the shield portion 53b. The detection portion and the magnetic encoder 56 oppose each other via the protective cover 53 with a predetermined air gap therebetween. The fitting portion 53a of the protective cover 53 has a cylindrical portion 58 adapted to be metal-contact fit into a fitting surface 51a formed on the inner circumference of the end of the outer member 51. A radially reduced cylindrical portion 59 axially extends from the cylindrical portion 58. In addition, an elastic member 60, of synthetic rubber, is integrally adhered to the radially reduced portion 59 via vulcanizing adhesion. The elastic member 60 is adhered to the radially reduced portion 59 so that it does not interfere with the rotation speed sensor 57 projecting from the side-face of the shield portion 53b of the protective cover 53. In addition, the elastic member 60 has an annular projection 60a projecting radially outward from the outer circumference of the cylindrical portion 58. The annular projection 60a is press-contacted against the inner circumference of the end of the outer member 51 during fitting of the protective cover 53. This improves sealability.
These protective covers 53 are usually stacked upon each other to save storage space and stocked to await the next manufacturing step as shown in FIG. 13(a). In this case, in order to prevent the stacked protective covers 53 from being fit in each other before the elastic members 60 are vulcanizing adhered to the protective covers 53, an inner diameter d1 (FIG. 12) of the cylindrical portion 58 of the fitting portion 53a is set smaller than an outer diameter d2 of the radially reduced portion 59 (d1<d2). This also makes it possible to prevent the “fitting in” of the protective covers 53 even after vulcanizing adhesion of the elastic members 60 as shown in FIG. 13(b). Thus, this further improves the workability during manufacture of the protective covers 53 (see, JP 2012-202415 A).
In the wheel bearing apparatus, an elastic member 60 of synthetic resin is integrally adhered to the radially reduced portion 59. It has an annular projection 60a projecting radially outward from the outer circumference of the cylindrical portion 58 of the fitting portion 53a. The annular projection 60a is elastically deformed and press-contacted against the inner circumference of the outer member 51. The protective cover 53 is fit into the outer member 51. Thus, it is possible to improve the sealability of the fitting portion 53a. However, it is a problem of the protective cover 53 that the elastic member 60 is pushed out toward the inner-side and it bulges out from the end face of the outer member 51 when the protective cover 53 is press-fit into the outer member 51. Accordingly, the sealability is impaired. In order to solve this problem, an elastic member has been developed that is integrally formed with a lip that elastically contacts against the inner circumference of the end of the outer member 51. However, another problem is caused in that the newly developed elastic member would sometimes be damaged or cut by metallic portions of the protective cover when the protective covers are stacked upon each other during the manufacturing steps of the protective covers.